Vessel arrangement

ABSTRACT

A vessel ( 100 ) having a stabilization arrangement, the stabilization arrangement having a first tank ( 10 ) and a second tank ( 11 ), each of the first and second tanks ( 10, 11 ) configured to hold a water column, a channel ( 12, 22 ) connecting the first tank ( 10 ) to the second tank ( 11 ), and a turbine unit ( 13, 23, 33, 34 ) arranged in the channel ( 12, 22 ).

The present invention relates to an arrangement for a vessel, such as a ship, and more particularly to systems and methods for the operation of a vessel.

BACKGROUND

The maritime industry faces continuous demands for improved technology in relation to the operation of ships or other types of vessels, such as rigs or special-purpose vessels. This includes, for example, requirements for improved safety, improved energy efficiency and reduced emissions levels, resulting from both regulatory and market demands.

For example, various configurations of hybrid or full-electric propulsion systems have been proposed and/or developed. Also, alternative energy sources, such as LNG, are being investigated, as well as utilisation of renewable resources, both directly, for example through Flettner rotors, or indirectly through, for example, sustainable fuels such as hydrogen or biofuels.

The inventors are also involved in various such initiatives, and the present disclosure has the objective to provide systems and methods for the design and/or operation of ships which provides advantages over known solutions and techniques in terms of energy efficiency, safety, passenger or crew comfort, or other aspects.

SUMMARY

In an embodiment, there is provided a vessel having a stabilization arrangement, the stabilization arrangement having a first tank and a second tank, each of the first and second tanks configured to hold a water column, and a first channel connecting a lower part of the first tank to a lower part of the second tank, wherein the vessel comprises at least one of:

-   -   a first turbine unit arranged in the first channel;     -   a second channel arranged to connect an upper part of the first         tank to an upper part of the second tank, and a second turbine         unit arranged in the second channel;     -   a third turbine unit arranged in the upper part of the first         tank;     -   a fourth turbine unit arranged in the upper part of the second         tank.

In an embodiment, there is provided a vessel having an internal moon pool, a fluid channel extending from the moon pool to an outside of the vessel, a fluid turbine unit arranged in the fluid channel, the fluid turbine unit comprising a fluid turbine coupled to a generator.

In an embodiment, there is provided a vessel having a hull comprising at least one fluid channel, each channel having a first opening and a second opening to an outside of the hull, and each channel having a turbine unit disposed therein, the turbine unit comprises a fluid turbine coupled to a generator.

The detailed description below and the appended claims outline further embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments will now be described with reference to the appended drawings, in which:

FIG. 1 illustrates a stabilization arrangement for a vessel according to an embodiment.

FIG. 2 illustrates a stabilization arrangement for a vessel according to an embodiment.

FIG. 3 illustrates a stabilization arrangement for a vessel according to an embodiment.

FIG. 4 illustrates a stabilization arrangement for a vessel according to an embodiment.

FIG. 5 illustrates a turbine unit according to an embodiment.

FIG. 6 illustrates a power distribution network for a vessel.

FIG. 7 illustrates a stabilization arrangement for a vessel according to an embodiment.

FIG. 8 illustrates a stabilization arrangement for a vessel according to an embodiment.

FIG. 9 illustrates a turbine unit according to an embodiment.

FIG. 10 illustrates a vessel according to an embodiment.

FIG. 11 illustrates a vessel according to an embodiment.

FIG. 12 illustrates a vessel according to an embodiment.

FIG. 13 illustrates a turbine unit according to an embodiment.

FIG. 14 illustrates a power distribution network for a vessel.

FIG. 15 illustrates a turbine unit according to an embodiment.

FIG. 16 illustrates a vessel according to an embodiment.

FIG. 17 illustrates a turbine unit according to an embodiment.

FIG. 18 illustrates a power distribution network for a vessel.

FIG. 19 illustrates aspects of a vessel according to an embodiment.

FIG. 20 illustrates a turbine unit according to an embodiment.

DETAILED DESCRIPTION

FIG. 1 shows a sectional, cut view of a vessel 100 according to one embodiment. The vessel 100 has a roll stabilization arrangement with a first tank 110 and a second tank 111, which are configured to hold a water column. A channel 112 connects a lower part 110 a of the first tank 110 to a lower part 111 a of the second tank 111. Such a roll stabilisation arrangement will be familiar to those skilled in the art; as the vessel 100 rolls, the fluid (typically water) in the tanks 110, 111 and the channel 112 will move cyclically between the tanks 110, 111 with substantially the same frequency as the roll motion. The tanks 110, 111 are designed such that the movement of the water is out of phase with the roll motion, and such that the tanks produce a righting moment on the ship. The tanks 110, 111 and the channel 112 may be placed above or below the ship's metacentre (roll centre) 101. Generally, such a passive roll stabilisation arrangement can reduce roll by typically 40-60%.

According to the embodiment shown in FIG. 1, a liquid turbine unit 113 is arranged in the channel 112. The liquid turbine unit 113 may be any type of rotodynamic machinery, for example can the liquid turbine unit 113 comprise a water turbine, a propeller, or the like. Some embodiments of turbine units 113 will be described below.

FIG. 2 shows an alternative embodiment, where the vessel 100 has a second channel 122 arranged to connect an upper part 110 b of the first tank 110 to an upper part 111 b of the second tank 111. A gas turbine unit 123 is arranged in the second channel 122. In this embodiment, no liquid turbine unit is arranged in the channel 112. The tanks 110, 111 and the channels 112, 122 form a closed volume, such that a liquid movement from e.g. the first tank 110 to the second tank 111 will force an equivalent volume of gas (generally air) through the second channel 122 and through the gas turbine unit 123. The gas turbine unit 123 may be of various different designs and many types of rotodynamic machinery may be suitable for this purpose.

FIG. 3 shows yet another embodiment according to the present invention. In FIG. 3, a gas turbine unit 133 is arranged in the upper part 110 b of the first tank 110 and another gas turbine unit 134 arranged in the upper part 111 b of the second tank 111. The tanks 110, 111 are open to the atmosphere by vent ducts 135 and 136, respectively. As above, as the water moves between the tanks 110, 111, air will be forced through the turbine units 133, 134.

In the embodiment shown in FIG. 3, a liquid turbine unit 113 is arranged in the channel 112, in addition to the turbine units 133, 134. This is optional, however may be advantageous in that the operation of the individual turbines may be controlled in the most efficient or optimal manner.

FIG. 4 shows another embodiment, wherein a liquid turbine unit 113 is arranged in the channel 112 and gas turbine units 123 are arranged in the second channel 122.

FIG. 5 illustrates one possible embodiment of a turbine unit 113, 123, 133, 134. In this embodiment, the turbine unit 113, 123, 133, 134 comprises a propeller 114 coupled to an electric generator 115. Any type of fluid turbine 114 may be used, and this unit may be chosen based on the fluid (gas or liquid) and projected flow rates through the turbine unit, using conventional design methods. The generator 115 may be electric, as in this embodiment, but may also be of a different type, such as a hydraulic generator.

By means of any of the embodiments described above, it is therefore possible to generate power, such as electric power, from the oscillating fluid flow through one or more of the turbine units 113, 123, 133, 134. This energy may, for example, be utilised by the vessel, as described below.

One or more of the turbine units 113, 123, 133, 134 may further comprise a control unit 125 which is configured for regulating the torque acting from the generator 115 on the turbine 114. In this manner, the flow resistance through the turbine unit 113, 123, 133, 134 can be regulated, and thereby the electrical power generated as well as the damping effect of the roll stabilization arrangement on the vessel. In an electric machine, for example, the torque can be regulated very accurately and very quickly. By permitting control of this variable, improved stabilisation performance can be achieved. Additionally, or alternatively, the amount of energy extracted from the oscillating fluid can be maximised for any operating conditions of the vessel.

The turbine unit 113, 123, 133, 134 may further comprise a guide vane 126 a, 126 b arranged to guide a fluid towards the fluid turbine 114. This may be arranged so as to give a narrower or smaller flow path for the fluid past the turbine 114, and thereby improved performance in terms of, for example, power generated or controllability of the flow resistance.

The vessel 100 may have a power distribution network 151, illustrated in FIG. 6, where at least one turbine unit 113, 123, 133, 134 is operatively coupled to the power distribution network 151 such as to allow power generated by the turbine unit 113, 123, 133, 134 to be supplied to the power distribution network 151. The vessel 100 may, for example, have engine generators 152, 153, such as diesel engines, operatively coupled to the power distribution network 151 in the usual manner. Alternatively, or additionally, the vessel 100 may have one or more battery units operatively coupled to the power distribution network 151. In the illustrated embodiment shown in FIG. 6, one battery 154 is coupled to the power distribution network 151 via an DC/AC converter 155. The vessel's 100 propulsion machines 156, 157 may further be operatively coupled to the power distribution network 151. In the illustrated embodiment shown in FIG. 6, the propulsion machines 156, 157 are electric motors coupled via shafts to propellers 156 a and 157 a.

By means of such an arrangement, one can, for example, reduce the load on the engine generators 152, 153, or the battery 154, by utilising power generated by the turbine unit 113, 123, 133, 134. This therefore provides advantages of, for example, reduced fuel consumption, reduced emissions, and/or longer battery life. The latter may be particularly advantageous on full-electric vessels (or hybrid-electric vessels with only minor emergency generator power).

In one embodiment, illustrated in a top view of the stabilization arrangement in FIG. 7, the vessel 100 comprises dual channels 112 and 142 connecting a lower part 110 a of the first tank 110 to a lower part 111 a of the second tank 111. A turbine unit 113 is arranged in channel 112, and one turbine unit 143 is arranged in channel 142. Channel 112 in this embodiment comprises a one-way valve 119 permitting flow only from the second tank 111 to the first tank 110, and channel 142 comprises a one-way valve 139 permitting flow only from the first tank 110 to the second tank 111.

This allows each turbine unit 113, 143 to be optimised for the given flow direction, and avoids the need for the turbine unit 113, 143 to handle flow in both directions. An equivalent arrangement can be used for the air channel, i.e. the connection between the upper parts of the tanks 110, 111.

The tanks 110, 111 and the channels 112, 122, 142 may be arranged spaced in a direction abeam the vessel 100, e.g. located on either side of the vessel. In this case, the channel 112, 122, 142 may extend between the tanks 110, 111 perpendicularly to the longitudinal direction (or nominal direction of travel) of the vessel 100. This is the configuration illustrated in the embodiments described above. In this configuration, the stabilization arrangement may reduce roll motion, and generate power based on the roll forces acting on the vessel 100.

Alternatively, or additionally, the tanks 110, 111 may be spaced in a longitudinal direction of the vessel 100. This is illustrated in FIG. 8. In this embodiment, the pitch motion of the vessel 100 may be damped and/or power may be generated based on pitch forces acting on the vessel 100. This embodiment may be particularly advantageous, for example, in stand-by or offshore supply vessels, which spend large amounts of operating time in stand-by mode. In this mode, the ship may control the yaw to weather vane into the incoming waves, thereby reducing roll, however the pitch motion may be a considerable discomfort for the crew. Further, according to this embodiment, the fuel consumption of the vessel 100 may be reduced during such stand-by mode.

The turbine unit 113, 123, 133, 134 can be a bidirectional turbine, i.e. a turbine configured for conversion of energy from an oscillating fluid stream. In one embodiment, the turbine unit 113, 123, 133, 134 can be configured to have a fixed direction of rotation, independent of the direction of fluid flow through the turbine unit 113, 123, 133, 134. This may be achieved, for example, by means of a Wells turbine or a Darrieus turbine. This provides the advantage that no moving parts are present in the channel 112, 122, 142 (with the exception of the rotary part of the turbine unit itself), which improves system reliability. In an alternative embodiment, the turbine unit 113, 123, 133, 134 may have a propeller 114 with variable pitch blades. The variable pitch blades may be actively controlled, or they may be passively controlled via the fluid stream, e.g. with a pivot so that the blades automatically turn in response to a change in fluid flow direction.

An embodiment with variable pitch blades is illustrated in FIG. 9. The fluid turbine 114′ has controllable-pitch blades. A pitch controller, in this embodiment embedded in the control unit 125, controls the pitch of the blades. This permits the use of an optimal pitch for any operating condition, such as to maximize power generation or to obtain any desirable dampening performance by using the pitch to adjust the resistance for the fluid in the channel.

Preferably, the blades can be rotated at least 180 degrees. This allows the generator 115 to maintain a given rotational direction, while the blade pitch is used to account for directional changes in the flow. This allows a more optimized generator design, in that it does not have to be designed for oscillating operation with changes in the rotational direction.

The pitch may be actively controlled via the pitch controller based on a sensor reading of the fluid flow in the channel 130, 131. The sensor 127 may be a flow meter, or any other sensor capable of providing a signal which is indicative of the flow in the channel. Alternatively, the pitch can be passively controlled, i.e. that the fluid flow itself turns the blades as the fluid flow oscillates.

FIG. 10 shows a sectional, cut view of a vessel 200 according to one embodiment. The vessel 200 has a moon pool 210 enclosed within its hull structure, where the moon pool 210 permits access to, for example, lower equipment or tools through the moon pool 210 to a subsea location. This may be, for example, subsea wellhead equipment, a remotely operated vehicle (ROV), a sea floor robot, or any other item needing to be deployed or suspended from the vessel 200 into the sea.

The vessel 200 has first and second fluid channels 211, 221 extending from the moon pool 210 to an outside of the vessel 200. The moon pool 210 is otherwise a substantially closed volume, being defined by the hull structure of the vessel 200 and the water 201 on which the vessel 200 floats.

A fluid turbine unit 213, 223 is arranged in each fluid channel 211, 221. With reference to FIG. 13, each fluid turbine unit 213, 223 comprises a fluid turbine 214 coupled to a generator 215. In the embodiment described here, the generator 215 is an electric generator, however other types of generators are also possible, for example hydraulic generators. A control unit 225 is arranged with the generator 215 and configured for regulating a torque acting from the generator 215 on the turbine 214. This allows regulation of the resistance from the fluid turbine 214 on a fluid flow through the channel 211, 221, as well as optimisation of the operation of the turbine unit 213, 223 so as to maximise power extracted.

The fluid turbine unit 213, 223 may further comprise a guide vane 226 a, 226 b arranged to guide a fluid towards the fluid turbine 214. This may be arranged so as to give a narrower or smaller flow path for the fluid past the turbine 214, and thereby improved performance in terms of, for example, power generated or controllability of the flow resistance.

Again referring to FIG. 10, as the vessel 200 heaves in the water, the water column in the moon pool 210 will fluctuate upwards and downwards, as indicated by the double arrow. This movement forces air present in the moon pool 210 cyclically through the fluid channels 211, 221 and past the turbine units 213, 223, during which power can be generated by the generator 215.

In one embodiment, illustrated in FIG. 11, the vessel 200 comprises a ventilation shaft 230 having a valve 231. The ventilation shaft 230 extends from the moon pool 210 to the outside of the vessel 200. By means of the ventilation shaft 230, an opening to the outside atmosphere can be selectively provided, for example to avoid (or reduce) pressure fluctuations in the moon pool 210 when workers are carrying out operations in the moon pool 210 area, or when no power generation through the turbine units 213, 223 is required. Alternatively, the turbine units 213, 223 and/or the channels 211, 221 can be arranged so that they selectively provide a free opening to the outside atmosphere, for example by letting air bypass the turbine units 213, 223, for the same purpose.

In one embodiment, illustrated in FIG. 12, the first fluid channel 211 comprises a first one-way valve 219 permitting flow from the moon pool 210 to the outside of the vessel 200 and the second fluid channel 221 comprises a second one-way valve 239 permitting flow from the outside of the vessel 200 to the moon pool 219.

This ensures that air drawn into the moon pool 210 flows through the second channel 221 and past the second turbine unit 223, while air flowing out of the moon pool 210 flows through the first channel 211 and past the first turbine unit 211. This allows the turbine units 213, 223 to be optimised in their design for handling flow in one direction only, which allows for a more efficient design. (As opposed to a turbine unit having to be designed for flow in both directions.)

By means of any of the embodiments described above, it is therefore possible to generate power, such as electric power, from the oscillating fluid flow through one or more of the turbine units 213, 223. This energy may, for example, be utilised by the vessel, as described below.

The vessel 200 may have a power distribution network 251, illustrated in FIG. 14, where at least one turbine unit 213, 223 is operatively coupled to the power distribution network 251 such as to allow power generated by the turbine unit 213, 223 to be supplied to the power distribution network 251. The vessel 200 may, for example, have engine generators 252,253, such as diesel engines, operatively coupled to the power distribution network 251 in the usual manner. Alternatively, or additionally, the vessel 200 may have one or more battery units operatively coupled to the power distribution network 251. In the illustrated embodiment shown in FIG. 14, one battery 254 is coupled to the power distribution network 251 via an DC/AC converter 255. The vessel's 200 propulsion machines 256, 257 may further be operatively coupled to the power distribution network 251. In the illustrated embodiment shown in FIG. 14, the propulsion machines 256, 257 are electric motors coupled via shafts to propellers 256 a and 257 a.

By means of such an arrangement, one can, for example, reduce the load on the engine generators 252, 253, or the battery 254, by utilising power generated by the turbine unit 213, 223. This therefore provides advantages of, for example, reduced fuel consumption, reduced emissions, and/or longer battery life. The latter may be particularly advantageous on full-electric vessels (or hybrid-electric vessels with only minor emergency generator power).

The turbine unit 213, 223 can be a bidirectional turbine, i.e. a turbine configured for conversion of energy from an oscillating fluid stream. In one embodiment, the turbine unit 213, 223 can be configured to have a fixed direction of rotation, independent of the direction of fluid flow through the turbine unit 213, 223. This may be achieved, for example, by means of a Wells turbine or a Darrieus turbine. This provides the advantage that no moving parts are present in the channel 211, 221 (with the exception of the rotary part of the turbine unit itself), which improves system reliability. In an alternative embodiment, the turbine unit 213, 223 may have a propeller 214 with variable pitch blades. The variable pitch blades may be actively controlled, or they may be passively controlled via the fluid stream, e.g. with a pivot so that the blades automatically turn in response to a change in fluid flow direction.

An embodiment with variable pitch blades is illustrated in FIG. 15. The fluid turbine 214′ has controllable-pitch blades. A pitch controller, in this embodiment embedded in the control unit 225, controls the pitch of the blades. This permits the use of an optimal pitch for any operating condition, such as to maximize power generation to adjust the resistance for the fluid in the channel.

Preferably, the blades can be rotated at least 180 degrees. This allows the generator 215 to maintain a given rotational direction, while the blade pitch is used to account for directional changes in the flow. This allows a more optimized generator design, in that it does not have to be designed for oscillating operation with changes in the rotational direction.

The pitch may be actively controlled via the pitch controller based on a sensor reading of the fluid flow in the channel 211, 221. The sensor 227 may be a flow meter, or any other sensor capable of providing a signal which is indicative of the flow in the channel. Alternatively, the pitch can be passively controlled, i.e. that the fluid flow itself turns the blades as the fluid flow oscillates.

In an embodiment, illustrated in FIG. 16, there is provided a vessel 300 having a hull 301. A pair of fluid channels 330, 331 are arranged in the hull 301, each fluid channel 330, 331 having openings in each end to the outside of the hull 301. One opening 330 a, 331 a of each channel 330, 331 is located below a nominal waterline 302 of the vessel 300. The other opening 330 b, 331 b may be arranged above or below the waterline 302. In the embodiment shown, the second opening 330 b of channel 330 is located below the waterline 302 and the second opening 331 b of channel 331 is located above the waterline 302.

A fluid turbine unit 313, 323 is arranged in each fluid channel 330, 331. With reference to FIG. 17, each fluid turbine unit 313, 323 comprises a fluid turbine 314 coupled to a generator 315. The turbine unit 313, 323 may comprise any type of rotodynamic machinery, for example can the turbine unit 313, 323 comprise a water turbine, a propeller, or the like. The turbine unit 313, 323 may be configured for operation with a liquid (e.g. seawater), a gas (e.g. air), or both, depending on the configuration and placement of the turbine unit 313, 323 in the fluid channel 330, 331. In the embodiment described here, the generator 315 is an electric generator, however other types of generators are also possible, for example hydraulic generators.

The fluid turbine unit 313, 323 may further comprise a guide vane 326 a, 326 b arranged to guide a fluid towards the fluid turbine 314. This may be arranged so as to give a narrower or smaller flow path for the fluid past the turbine 314, and thereby improved performance in terms of, for example, power generated or controllability of the flow resistance.

As the vessel 300 moves in the sea, an oscillating flow of water and/or air will be induced in the channels 330, 331. By means of the turbine unit 313, 323, it is possible to generate power, such as electric power, from this oscillating fluid flow through the channels 330, 331. This energy may, for example, be utilised by the vessel, as described below.

The channels 330, 331 may be arranged at a front part or an aft part of the vessel 300. This may be particularly beneficial to utilise the effects of pitch motion of the vessel 300. This may, for example, provide advantages in offshore stand-by vessels, which spend a lot of operating time weather vaning against incoming (often heavy) seas.

One or more of the turbine units 313, 323 may further comprise a control unit 325 which is configured for regulating the torque acting from the generator 315 on the turbine 314. In this manner, the flow resistance through the turbine unit 313, 323 can be regulated, and thereby the power generation through the turbine unit 313, 323 can be optimised. In an electric machine, for example, the torque can be regulated very accurately and very quickly. By permitting control of this variable, improved efficiency can be achieved and the amount of energy extracted from the oscillating fluid can be maximised for any operating conditions of the vessel.

The turbine unit 313, 323 may further comprise a guide vane 326 a, 326 b arranged to guide a fluid towards the fluid turbine 314. This may be arranged so as to give a narrower or smaller flow path for the fluid past the turbine 314, and thereby improved performance in terms of, for example, power generated or controllability of the flow resistance.

The vessel 300 may further have a power distribution network 351, illustrated in FIG. 18, where at least one turbine unit 313, 323 is operatively coupled to the power distribution network 351 such as to allow power generated by the turbine unit 313, 323 to be supplied to the power distribution network 351. The vessel 300 may have engine generators 352, 353, such as diesel engines operatively coupled to the power distribution network 351 in the usual manner. Alternatively, or additionally, the vessel 300 may have one or more battery units operatively coupled to the power distribution network 351. In the illustrated embodiment, one battery 354 is coupled to the power distribution network 351 via a DC/AC converter 355. The vessel's 300 propulsion machines 356, 357 may further be operatively coupled to the power distribution network 351. In the illustrated embodiment, the propulsion machines 356, 357 are electric motors coupled via shafts to propellers 356 a and 357 a.

By means of such an arrangement, one can, for example, reduce the load on the engine generators 352, 353, or the battery 354, by utilising power generated by the turbine unit 313, 323. This therefore provides advantages of, for example, reduced fuel consumption, reduced emissions, and/or longer battery lifetime. The latter may be particularly advantageous on full-electric vessels (or hybrid-electric vessels having only minor emergency generator capacity).

In one embodiment, illustrated in FIG. 19, the opening 330 a, 331 a has an area which is larger than a cross-sectional area of the channel 330, 331. The area may be, for example, more than twice, three times, four times, five times, or ten times the cross-sectional area of the channel 330, 331. This enhances the fluid flow through the channel 330, 331, as a larger amount of fluid will enter/exit the opening 330 a, 331 a at each cycle.

The turbine unit 313, 323 can be a bidirectional turbine, i.e. a turbine configured for conversion of energy from an oscillating fluid stream. In one embodiment, the turbine unit 313, 323 can be configured to have a fixed direction of rotation, independent of the direction of fluid flow through the turbine unit 313, 323. This may be achieved, for example, by means of a Wells turbine or a Darrieus turbine. This provides the advantage that no moving parts are present in the channel 330, 331 (with the exception of the rotary part of the turbine unit itself), which improves system reliability. In an alternative embodiment, the turbine unit 313, 323 may have a propeller 314 with variable pitch blades. The variable pitch blades may be actively controlled, or they may be passively controlled via the fluid stream, e.g. with a pivot so that the blades automatically turn in response to a change in fluid flow direction.

An embodiment with variable pitch blades is illustrated in FIG. 20. The fluid turbine 314′ has controllable-pitch blades. A pitch controller, in this embodiment embedded in the control unit 325, controls the pitch of the blades. This permits the use of an optimal pitch for any operating condition, such as to maximize power generation to adjust the resistance for the fluid in the channel.

Preferably, the blades can be rotated at least 180 degrees. This allows the generator 315 to maintain a given rotational direction, while the blade pitch is used to account for directional changes in the flow. This allows a more optimized generator design, in that it does not have to be designed for oscillating operation with changes in the rotational direction.

The pitch may be actively controlled via the pitch controller based on a sensor reading of the fluid flow in the channel 330, 331. The sensor 327 may be a flow meter, or any other sensor capable of providing a signal which is indicative of the flow in the channel. Alternatively, the pitch can be passively controlled, i.e. that the fluid flow itself turns the blades as the fluid flow oscillates.

Embodiments described here may be particularly advantageous, for example, in stand-by or offshore supply vessels, which spend large amounts of operating time in stand-by mode. In this mode, the ship may control the yaw to weather vane into the incoming waves, thereby reducing roll, however the pitch motion may then be significant. The energy consumption of the vessel 100, 200, 300 may thereby be reduced during such stand-by mode. However the invention is not limited to any particular type of vessel, and may be employed in a wide variety of applications.

When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

The present invention is not limited to the embodiments described herein; reference should be had to the appended claims. 

1. A vessel having a stabilization arrangement, the stabilization arrangement having a first tank and a second tank, each of the first and second tanks configured to hold a water column, and a first channel connecting a lower part of the first tank to a lower part of the second tank, wherein the vessel comprises at least one of: a first turbine unit arranged in an upper part of the first tank; and a second turbine unit arranged in an upper part of the second tank, and wherein the first and second turbine units each comprises a fluid turbine coupled to a generator.
 2. A vessel according to claim 1, further comprising a power distribution network, wherein at least one of the first and second turbine units is operatively coupled to the power distribution network such as to allow power generated by the turbine unit to be supplied to the power distribution network.
 3. (canceled)
 4. A vessel according to claim 1, wherein the first and second turbine units comprises a control unit configured for regulating a torque acting from the generator on the turbine.
 5. A vessel according to claim 1, wherein the first and second turbine units comprises a guide vane arranged to guide a fluid towards the fluid turbine.
 6. A vessel according to claim 1, wherein the first tank and the second tank are spaced in a direction abeam the vessel. 7-10. (canceled)
 11. A vessel according to claim 6, wherein the fluid turbine is configured to have a fixed direction of rotation, independent of the direction of fluid flow through the turbine unit.
 12. A vessel according to claim 1, wherein the fluid turbine comprises variable pitch blades.
 13. (canceled)
 14. A vessel according to claim 12, wherein the first and second turbine units comprises a pitch controller and a sensor, the sensor arranged to provide a signal indicative of the fluid flow rate through the respective turbine unit and the pitch controller arranged to control the pitch of the blades in response to the signal. 15-29. (canceled)
 30. A vessel having a hull comprising at least one fluid channel, each channel having a first opening and a second opening to an outside of the hull, and each channel having a turbine unit disposed therein, the turbine unit comprises a fluid turbine coupled to a generator.
 31. A vessel according to claim 30, wherein the first opening is located below a waterline of the vessel.
 32. A vessel according to claim 31, wherein the second opening is located below the waterline.
 33. A vessel according to claim 31, wherein the second opening is located above the waterline.
 34. A vessel according to any of claims 30, wherein the at least one fluid channel is arranged in a front section of the hull.
 35. A vessel according to claim 34, wherein the at least one fluid channel comprises a first fluid channel and a second fluid channel, and the first fluid channel is arranged in the front section of the hull and the second fluid channel is arranged in the aft section of the hull.
 36. A vessel according to any of claims 30, wherein the first opening has an area which is larger than a cross-sectional area of the channel. 37-47. (canceled)
 48. A vessel having a stabilization arrangement, the stabilization arrangement having a first tank and a second tank, each of the first and second tanks configured to hold a water column, and a first channel connecting a lower part of the first tank to a lower part of the second tank, wherein the vessel comprises: a second channel arranged to connect an upper part of the first tank to an upper part of the second tank, and a turbine unit arranged in the second channel; and wherein the turbine unit comprises a fluid turbine coupled to a generator.
 49. A vessel according to claim 48, further comprising a power distribution network, whereby the turbine unit is operatively coupled to the power distribution network such as to allow power generated by the turbine unit to be supplied to the power distribution network.
 50. A vessel according to claim 48, wherein the turbine unit comprises a control unit configured for regulating a torque acting from the generator on the turbine.
 51. A vessel according to claim 48, wherein the turbine unit comprises a guide vane arranged to guide a fluid towards the fluid turbine.
 52. A vessel according to claim 48, wherein the first tank and the second tank are spaced in a direction abeam the vessel. 